space physics

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  • space physics
    • the life cycle of stars
      • nebula - cloud of dust and gas
        • the force of gravity pulls it together to form a...
          • protostar
            • as the star gets denser, the temperature rises and more particles collide with each other
              • when the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
                • this gives out huge amounts of energy, which keeps the core of the star hot. a star is born
                  • main sequence star
                    • the star enters a long stable period, outward pressure caused by the nuclear fusion (trying to expand the star) balances the force of gravity (pulling everything inwards)
                    • typically lasts several billion years
                    • eventually, hydrogen begins to run out and the star swells into
                      • red super giant
                        • if it was larger star
                        • it becomes red because the surface cools.
                        • fusion of helium and other elements occurs. heavier elements (e.g. Fe) are created in the core of the star
                        • it starts to glow brightly again, as it undergoes more fusion and expands and contracts several times, forming elements as heavy as iron
                          • eventually they explode into a
                            • supernova
                              • forming elements heavier than iron and ejecting them into the universe to form new planets and stars
                              • this throws the outer layers of dust and gas into space, leaving a very dense core called a
                                • neutron star
                                • if the star is massive enough, it will become a
                                  • black hole
                                    • a super dense point in space that not even light can escape from
                      • red giant
                        • if its was small star
                        • it becomes red because the surface cools.
                        • fusion of helium and other elements occurs. heavier elements (e.g. Fe) are created in the core of the star
                        • it becomes unstable and ejects its outer layer of dust and gas
                          • this leaves behind a hot, dense, solid core - a
                            • white dwarf
                              • as this cools down, it emits less and less energy
                                • when it no longer emits a significant amount of energy it is called a
                                  • black dwarf
      • stars and their life cycles produce and distribute all naturally occurring elements
    • the solar system
      • the sun is the centre of our solar system. it is orbited by:
        • planets
          • large objects that orbit a star
          • 8 in our solar system
          • must be large enough to have "cleared their neighbourhoods"
            • meaning their gravity must be strong enough to have pulled in any nearby objects apart from their satellites
        • moons
          • orbit planets
          • a type of natural satelilte
        • dwarf planets
          • e.g. pluto
          • planet like objects that orbit stars but don't meet all the rules for being a planet
        • artificial satellites
          • satellites built by humans
          • generally orbit earth
      • part of the milky way - a massive collection of billions of stars that are all held together by gravity
      • satellite - an object that orbits a second, more massive object
    • orbits
      • the size of the orbit depends on the object's speed
        • the closer you get to a star or a planet, the stronger the gravitational force is
        • the stronger the force, the faster the orbiting object needs to travel to remain in orbit
          • to not crash into the object that it's orbiting
        • for an object in stable orbit, if the speed of the object changes, the radius of its orbit must do so too.
          • faster moving objects will move in a stable orbit with a smaller radius than slower moving ones
      • gravity provides the force that creates orbits
        • the planets orbit around the sun in almost circular orbits
          • the same goes for the moon around the earth
          • if an object is travelling in a circle, it is constantly changing direction
            • so it is constantly accelerating
            • so it is constantly changing velocity (but NOT speed)
            • for an object to accelerate, there must be a force acting on it
              • this force is directed towards the centre of the circle
              • this force would cause the object to just fall towards whatever it was orbiting
                • but as the object is already moving, it just causes it to change direction
                • the object keeps accelerating towards what it's orbiting but the instantaneous velocity (right angles to the acceleration) keeps it travelling in a circle
                  • the force that makes this happen is provided by the gravitational force between the planet and the sun
                    • or between the planet and its satellites
    • red shift and the big bang
      • the universe seems to be expanding
        • this evidence suggests the universe started with a bang
          • new evidence might change theories
            • big bang is the best guess so far
            • whenever scientists discover new evidence, they either have to make a new theory or change a current on to explain what they've observed
            • there is still lots that scientists don't know about the universe
            • observations of supernovae from 1998 to the present day appear to show that distant galaxies are receding at an increasing speed
            • currently, scientists think that the universe is mostly made up of dark matter and dark energy
              • dark matter is the name given to an unknown substance which holds galaxies together but does not emit any electromagnetic radiation
              • dark energy is thought to be responsible for the accelerated expansion of the universe
            • no one really knows what dark matter and dark energy are so there are lots of different theories about it
              • these theories get tested over time and are either accepted or rejected.
          • something must have made the universe expanding
          • initially all the matter in the universe occupied a very small space. this tiny space was very dense and so was very hot
          • then it 'exploded' - space started expanding, and the expansion is still going on
        • when we look at light from most distant galaxies, the wavelength has increased
          • the wavelengths are all longer than they should be - they're shifted towards the red end of the spectrum. this is called red shift
            • this suggests that the source of the light is moving away from us
              • measurements of the red-shift indicate that these distant galaxies are moving away from us (receding) very quickly - and it's the same result whichever way you look
                • more distant galaxies have greater red shifts than nearer ones - and so all galaxies are moving away from every other galaxy, not just ours
                  • the conclusion appears to be that the whole universe is expanding
        • analogy
          • a ballon covered with pompoms
            • as the balloon is inflated, it stretches
              • the pompoms mover further away from each other
                • the ballon represents the universe and each pompom is a galaxy
                  • as time goes on, space stretches and expands, moving the galaxies away from each other
                    • this is a simple model
                      • but it shows how the expansion of space makes it look like galaxies are moving away from us
                      • balloons only stretch so far
                      • there would be galaxies inside the balloon too

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